The present invention relates to a torsional damper of the type having damper elements resiliently coupled by a spring arrangement and a friction generating device. The torsional damper of this kind is advantageously used in transmitting torque between an internal combustion engine and a torque converter.
U.S. Pat. No. 4,904,225 issued to Worner et al., on Feb. 27, 1990 discloses damper elements coupled by a spring arrangement. The spring arrangement has an intermediate support connected resiliently to one damper element by long-stroke arcuate helicoidal springs and to the other damper element by short-stroke springs. Additionally, a friction generating device or slip coupling that exibits play is also arranged. The friction generating device is operative to generate frictional resistance that counteracts the movement of the damper elements.
A torsional damper has been proposed in copending U.S. patent application Ser. No. 08/301,568, filed Sep. 7, 1994, entitled "TORSIONAL DAMPER WITH FRICTION GENERATING DEVICE." This copending United States Application, having been commonly assigned herewith, claims priority based on Japanese Patent Application No. 5-222358 filed in Japan on Sep. 7, 1993. This torsional damper includes driver and driven damper elements resiliently coupled by a spring arrangement, and a friction generating device. The friction generating device includes a plurality of friction blocks received in a plurality of windows, respectively, of the driven damper elements with play in the circumferential direction of the driven damper element, and means on the driver damper element for biasing the plurality of friction blocks against a radially extending wall of the driver damper element. In operation, the friction blocks tend to be thrown radially outwardly to engage radially outer edges of the corresponding windows due to centrifugal force while the torsional damper rotates at high speeds. Owing to this engagement of the friction blocks with the edges of the windows, the friction blocks, the driven damper element entrains the friction blocks during relative rotation between the damper elements with small degrees below a predetermined degree even if the rotation of the driven damper element is not far enough to consume the movement play, generating frictional resistance that counteracts the movement of the driven damper element relative to the driver damper element.
An object of the present invention is to improve a torsional damper of this kind just mentioned with a friction generating device such that, during relative rotation between the damper elements within small degrees below a predetermined degree, the friction generating device does not offer frictional resistance that counteracts the relative rotation.